In accordance with predictions of dramatic increases in wireless data traffic in line with the recent vitalization of eco-systems related to the wireless Internet such as smartphones and app stores, spectrum sharing methods have attracted attention as methods of increasing frequency supply. However, with the current spectrum management system, demand for increased frequency supply could not be met promptly and frequency supply may also be limited. That is, refarming of exiting frequencies and frequency allocation to new providers through auctions may lead to inefficient use of time. Fundamentally, it has become more difficult to ensure new frequency bands in the table of frequency allocations.
Recently, as a method of solving these problems, a spectrum sharing method has drawn attention. Apologists for spectrum sharing see that the current lack of frequencies results from existing compartment-type spectrum management and can be overcome by spectrum sharing technology though frequencies seem to lack in the table of frequency allocations. However, spectrum sharing technology is not a new concept but various schemes have been employed as one of the resource management methods in communications systems in technical aspects. For example, cellular schemes and multiple access schemes such as TDMA and CDMA that have been widely used are included herein.
As the existing spectrum sharing schemes are carried out according to the same technical standards or under the control of providers, effective interference suppression is possible. However, since distributed spectrum sharing schemes including a cognitive radio (CR) that has been recently introduced may cause tragedy of commons or harmful interference due to uncontrolled frequency use, problems arise in terms of spectrum management and existing user protection, and these schemes do not relate to the purpose of the market-based spectrum policy that becomes the current spectrum management system.
However, the apologists for spectrum sharing believe that the existing user protection from interference and the problems arising from the uncontrolled frequency use can be overcome or controlled through policy and technical means such as technical regulations or standards.
Types of spectrum sharing schemes may be classified according to sharing “methods” and sharing “subject and object.” Here, specifically, sharing methods are interference avoidance schemes, and coexistence and cooperation models are considered. In terms of the sharing subject and object, types of spectrum sharing schemes can be divided into sharing among equals in which the subject and object have equal rights and primary-secondary sharing in which a primary user and a secondary user share spectrum.
First, with a model based on cooperation, separate protocols are present so that resource allocation and interference avoidance are possible through cooperation among all users. Resource allocation and interference avoidance may be carried out centrally by a base station or individually by respective users. Mobile communications systems based on CDMA or TDMA fall under the former, while ad-hoc systems fall under the latter.
On the other hand, with a model based on coexistence, each user carries out interference avoidance without resource allocation using common protocols. The currently commercialized technologies based on coexistence (or existence) may include wireless LAN and cordless phones, and overlay and underlay techniques can also be included herein. Between the above-described two models, the coexistence model passively involves resource allocation and interference control as compared to the cooperation model in terms of technology. Therefore, coexistence is likely to cause interference.